It is common to produce a rigid foamed synthetic resin such as a rigid polyurethane foam or a rigid polyisocyanurate foam (hereinafter referred to as “a rigid foam”) by reacting a polyol component with a polyisocyanate component in the presence of a blowing agent, etc., and use it as a heat-insulating material having closed cells. As a blowing agent to be used for such a rigid foam, a hydrofluorocarbon compound or a hydrocarbon compound having a low boiling point is mainly used.
With respect to a rigid foam, further density reduction of the foam is desired in order to reduce the cost or the weight by reducing the amount of the raw material to be used. However, there is a problem such that along with the density reduction of a foam, the strength of the foam tends to decrease, and the dimensional stability is likely to deteriorate such that the rigid foam represented by a board is likely to undergo shrinkage.
Further, in consideration of a load to the environment, it has been studied to reduce a low boiling point hydrofluorocarbon compound and increase water, or in consideration of the flammability, it has been studied to reduce a hydrocarbon compound and increase water, or a technique has been studied to use only water as a blowing agent without using a low boiling point hydrofluorocarbon compound or hydrocarbon compound.
However, in a case where density reduction of a foam is attempted by using water in combination, or density reduction of a foam is attempted by water-foaming by carrying out foaming by means of only water, the foam tends to be remarkably susceptible to shrinkage, thus leading to deterioration in dimensional stability of the foam.
In order to attain both the density reduction and the dimensional stability, it is conceivable to make cells of the foam to be open cells. However, if cells are made to be open cells, heat-insulating properties will be poor, although the dimensional stability may thereby be improved.
Further, as prior art to prevent shrinkage of a foam to maintain the dimensional stability, a method is known wherein a polymer-dispersed polyol is added to a polyol compound to produce a rigid foam (Patent Documents 1 and 2). The polymer-dispersed polyol is a polyol having polymer particles dispersed in a polyol such as a polyether polyol or a polyester polyol, and it has been used in many cases as a raw material for polyurethane foams such as flexible foams or semi-rigid foams, in order to improve the mechanical properties of such polyurethane foams.
Further, as a case where a polyurethane foam is produced by using an amino-modified silicone, a method for producing a polyurethane foam for abrasive sheet, wherein cell diameters of the foam are widely distributed (Patent Document 3), a method to provide an elastic member having a small frictional resistance on its surface and having fine cells Patent Document 4), or a method for producing a polyurethane having excellent moldability and appearance, when molded by a reaction injection molding method (Patent Document 5), is known.
However, each of such cases disclosed in Patent Documents 3 to 5 is a technique relating to the production of a flexible polyurethane foam and thus is different from the present invention in the object and application.    Patent Document 1: JP-A-57-25313    Patent Document 2: JP-A-11-302340    Patent Document 3: JP-A-2004-75700    Patent Document 4: JP-A-2002-187929    Patent Document 5: JP-A-57-117524